High output operating apparatus for a fluorescent lamp

ABSTRACT

A high output operating circuit for a fluorescent lamp includes, in one embodiment, a magnetic circuit formed by confronting Ecores and having a pair of outer legs and a center leg. A pair of lamp current control windings are wound on the outer legs, and a cathode preheating compensation winding and a pair of cathode heating windings are wound on the center leg. The flux from the current control windings are in opposition in the center leg. The compensation winding is connected across the lamp between the cathodes by a glow starter. During preheating, the glow starter is closed, and the flux from the compensation winding superposed in the center leg provides optimum cathode preheating. When the lamp is operating, the glow starter is open, and the opposed flux in the center leg provides optimum cathode heating. In a second embodiment, a lamp current control winding, a pair of cathode heating windings, and a preheating compensation winding are wound on a common magnetic circuit. A pair of manually operated switches connect the windings in series with the lamp cathodes to provide optimum cathode preheating. During operation, the switches remove the compensation winding from the circuit and connect the cathode heating windings across the cathodes to provide optimum cathode heating.

Unite States Ptet 1 Nozawa et al.

[ 5] Apr. 17, 1973 [73] Assignee: Blackwell Electronics Ind. Co., Ltd.,

Shimogyo-ku, Kyoto, Japan [22] Filed: Apr. 27, 1971 [21] Appl. No.:137,781

[30] Foreign Application Priority Data Nov. 30, 1970 Japan ..45/105644[52] US. Cl. ..315/99, 315/106, 315/278, 315/290, 315/D1G.5 [51] Int.Cl. ..H05b 41/14 [58] Field of Search ..3l5/98, 99, 105,

315/106, 278, DIG. 5, 290

[56] References Cited UNITED STATES PATENTS 3,114,076 12/1963 Kobayashi..3l5/l05 X 3,047,772 7/1962 Kobayashi ..315/99 3,211,952 10/1965McMullen v.315/99 2,802,143 8/1957 Kobayashi ..3l5/278 FORElGN PATENTSOR APPLICATIONS 525,133 8/1940 Great Britain..... ..315/98 PrimaryExaminer-Palmer C. Demeo Attorney-Raphael Semmes ABSTRACT A high outputoperating circuit for a fluorescent lamp includes, in one embodiment, amagnetic circuit formed by confronting E-cores and having a pair ofouter legs and a center leg. A pair of lamp current control windings arewound on the outer legs, and a cathode preheating compensation windingand a pair of cathode heating windings are wound on the center leg. Theflux from the current control windings are in opposition in the centerleg. The compensation winding is connected across the lamp between thecathodes by a glow starter. During preheating, the glow starter isclosed, and the flux from the compensation winding superposed in thecenter leg provides optimum cathode preheating. When the lamp isoperating, the glow starter is open, and the opposed flux in the centerleg provides optimum cathode heating.

In a second embodiment, a lamp current control winding, a pair ofcathode heating windings, and a preheating compensation winding arewound on a common magnetic circuit. A pair of manually operated switchesconnect the windings in series with the lamp cathodes to provide optimumcathode preheating. During operation, the switches remove thecompensation winding from the circuit and connect the cathode heatingwindings across the cathodes to provide optimum cathode heating.

9 Claims, 3 Drawing Figures PATENTEDAPR1 H975 Nfl Nf2 INVENTORS SHUNICHI NOZAWA HISASHI KUROI MASAMICHI HATADA SHUNSAKU FUKUYAMA HIGH OUTPUTOPERATING APPARATUS FOR A FLUORESCENT LAMP BACKGROUND OF THE INVENTIONThe present invention relates to a high output operating system whichsupplies a hot cathode fluorescent lamp with more current than the ratedcurrent of the lamp but which, nevertheless, does not affect cathodelife adversely.

The object of the invention is to provide a high output operatingapparatus for glow starting and for manual starting, which can give thehighest output by minimizing cathode exhaustion of the fluorescent lamp,which is cheap in cost by being constructed with a simple magneticcircuit, and which, moreover, has superior utility by minimizing thenoise of the ballast.

The high output lighting circuits of the invention supply, through a lowinternal impedance cathode heating winding, a cathode heating voltagewhich is shifted by 90 degrees against lamp current and adjusted to anoptimum heating voltage corresponding to the case which provides thegreatest reduction of cathode exhaustion by the cathode heating effect,thus providing a substantially greater reduction of the cathodeexhaustion than that provided by ordinary equi-high impedance, ordinaryhigh impedance cathode heating circuits which are equivalent to highequi-impedance circuits in their function, or bi-pin shorted high outputcircuits.

In order to minimize the cathode exhaustion, in addition to thereduction of the cathode exhaustion by the cathode heating effect duringoperation, the invention is also concerned with the control of thecathode exhaustion during the starting of the lamp.

In general, it is well known that the cathode ex haustion, during thetime the fluorescent lamp is starting, considerably influences the lifeof the lamp. In order to minimize cathode exhaustion at starting, thefollowing requisites must be satisfied for a circuit of the preheatingstart type:

1. Upon impress of the starting pulse, the temperature should rapidlyfully rise so as to bring about full cathode emission; and

2. The amplitude of the starting pulse should not be excessive.

In the case in which the cathode is preheated by a voltage source, anyexcessive kick voltage induced at the time when the glow starter opensis absorbed and suppressed because of the fact that the cathodepreheating circuit forms a secondary closed circuit. An optimumpreheating voltage should be given to the cathode; otherwise, largerpreheating current from the voltage source will flow due to the factthat the resistance of the cathode filament is shorted by the cathodearc before the temperature of the cathode has fully risen. In the caseof a current source, the preheating current compensation winding isconnected in additive polarity; thus, any excessive kick voltage issuppressed, and the optimum preheating current is supplied by thepreheating current compensation winding. Now, the increase of cathodeexhaustion due to the fluctuation of source voltage will be reduced bymaking the cathode preheating independent of saturation of the magneticpath, which has been satisfied in both systems.

The magnetic circuit, which is simply constructed by confronting twoE-cores, has the benefit of providing a ballast having minimum noise,because in this kind of high output operating circuit, the capacity ofthe ballast reaches two or three times the rated lamp current. Moreover,this is useful for keeping the cost lower, bringing about a practicaladvantage.

SUMMARY OF THE INVENTION According to the invention, by means of anoptimum system satisfying all of the above requisites, a useful highoutput operating system can be provided, which can keep the cathodeexhaustion at a minimum.

Briefly, the invention contemplates the provision of a common magneticcircuit and lamp current control means, cathode heating windings, and acathode preheating compensating winding wound thereon. Switch meansconnects the compensating winding across the lamp for preheating anddisconnects the compensating winding during operation of the lamp. Thewindings are so wound and connected that during preheating, optimumpreheating voltage is supplied to the cathodes, and, during operation ofthe lamp, optimum heating voltage is supplied to the cathodes, and thecathode heating voltage is shifted ninety degrees from the lamp current.

In one embodiment, the magnetic circuit is formed by a pair ofconfronting E-cores and has a pair of outer legs and a center leg. Apair of lamp current control windings are wound on the outer legs andprovide flux in opposition in the center leg. The compensating windingand the cathode heating windings are wound on the center leg, and a glowstarter connects the compensation winding across the lamp forpreheating, at which time the winding contributes to the flux in thecenter leg. When the lamp begins operation, the glow starter opens andthe compensating winding is removed from the circuit.

- In a second embodiment, a lamp current control winding, a cathodepreheating compensation winding, and a pair of cathode heating windingswound in opposition to the control and compensation windings areconnected by a pair of manual switches in series with the lamp cathodesfor preheating. During lamp operation, the switches disconnect thecompensating winding and connect the cathode heating windings across therespective cathodes.

THE DRAWINGS The invention will more fully be understood from thefollowing descriptions taken in connection with the attached drawings,in which:

FIG. 1 is a circuit diagram showing an embodiment of the invention;

FIG. 2 shows the structure of magnetic circuit in the above circuit; and

FIG. 3 is a circuit diagram showing another embodiment of the invention.

The invention will now be described with reference to the attacheddrawings.

The circuit diagram shown in FIG. I is an embodiment of the inventionapplied in a glow starter system. As illustrated in FIG. 2, a magneticcircuit formed by confronting two E-cores E and E has a lamp currentcontrol winding divided into two windings N and N on left and right legs1 and 2, respectively, both cathode heating windings N and N for heatingthe cathodes and a compensation winding N for preheating the cathodesbeing wound on a center leg 3, As shown in FIG. 1, one end of thecontrol winding N is connected with one end a of a cathode filament 5 ofa fluorescent lamp 4, and one end of the control winding N is connectedwith one end of a cathode filament 6 of the lamp 4. Moreover, betweenone end of each cathode filament, that is, between a and c, compensationwinding N and a glow starter switch means 7 are connected in series. Twopairs of ends a, b and c, d are connected to both ends of cathodes 5 and6, respectively An A.C. source S is provided between the other ends ofwindings N, and N The operation of the invention will now be explainedin relation to the times when the lamp is operated and when the lamp ispreheated.

During the time the lamp is operated, compensation winding N will beleft ineffective as glow starter 7 stays open. A flux F (shown in fullline in FIG. 2) generated by control winding N is opposed to a flux F(shown in dotted line in FIG. 2) generated by control winding N atcenter leg 3 and is additive to it at two legs 1 and 2. In this case,the flux interlinking with cathode heating windings N and N has been setto a desired value by selecting a suitable combination of the number ofturns of control windings N,, N and the size of the core (which dependsupon the gaps formed between the confronting portions of each leg of thecores, the sectional area of each magnetic path, the length of the pathand so on) The reason why the flux'density in center leg 3 is lowered bypassing the fluxes in opposite directions is that, otherwise, in such asystem as the cathodes are heated by means of control windings N N on acommon magnetic path, during the time the lamp is operating, asufficient flux is hardly obtained in the course of preheating and,also, an input current in the preheating period becomes too large,bringing about remarkably poor economy.

In the preheating phase, when glow starter 7 closes, an input currentfor preheating will pass through lamp current control winding N cathodepreheating compensation winding N and lamp current control winding Ninducing cathode preheating voltages at cathode preheating windings Nand N In this case, also, the fluxes generated by control windings N Nwill function differentially'in center leg 3, but a flux F (shown in adot and dash line in FIG. 2) generated by compensation winding N will besuperimposed on the previous fluxes to induce a sufficient voltage forpreheating, from which an input current for preheating may be obtainedwhich is comparable to the lamp current at the operating phase, thusmaking economical use of the ballast capacity possible.

As described above, the invention provides sufficient cathode preheatingvoltage and cathode heating voltage by means of an economical structureof the magnetic circuit, both the cathode heating voltage and thepreheating voltage being adjusted to a desired optimum value. During thetime the lamp is operating, the cathode heating voltages induced in thecathode heating windings N and N are shifted by about 90 against thelamp current; and because a reluctance of the center leg is chosen to below as compared to reluctances of the right and the left legs, which iscontrary to the structure of leakage path in so-called leakagetransformers, a series inductance formed equivalently at the heatingwinding becomes very small, forming a low internal impedance circuit andthus exhibiting good branching characteristics.

The circuit shown in FIG. 3 is another embodiment of the inventionapplied to a type of manual start. In FIG. 3, a lamp current controlwinding 8, windings 9 and 10 for heating the cathodes, and an adjustingwinding 11 for preheating current are all wound around the same magneticpath 12. Switches 13 and 14, have ganged switch arms and 21, areprovided for determining the connections of windings 8, 9, 10, and 11 tothe cathodes 16 and 17 of fluorescent lamp 15. In a first position ofthe switch arms, as seen in FIG. 3, switch arms 20 and 21 are connectedto first fixed contacts 22 and 23 to connect an end of winding 9 tocathode 17 and an end of winding 10 to cathode 16, respectively.

- Switch arms 20 and 21 may be moved to a second position into contactwith second fixed contacts 24 and 25 to connect the opposite ends ofwinding 11 to cathodes 17 and 16, respectively. The lamp current controlwinding 8 is connected at one end thereof to a source 18, the other endthereof being connected to cathode heating winding 9 and fixed contact22 of switch 13. Two ends of cathode 17 are connected via switch 13 toboth ends of cathode heating winding 9, while two ends moved to thesecond position in contact with fixed contacts 24 and 25, respectively,current will flow from source 18 through winding 8, winding 9, cathode17, switch 13, winding 11, switch 14, cathode l6, winding 10, and switch19 back to source 18. Each winding 8, 9, 11, 10 will be connected inseries in the circuit as a single choke coil, and thus as ordinarypreheating circuit of switch start type will be formed. After thecathodes are preheated according to the above, switch arms 20 and 21 ofswitches 13 and 14 are switched into the first position in contact withfixed contacts 22 and 23, respectively. A current will then flow fromsource 18 through winding 8, winding 9 and cathode 17 in parallel,fluorescent lamp 15, cathode 16 and winding 10 in parallel, and switch19 back to source 18, providing current for an operating circuit. It isto be noted that cathode heating windings 9 and 10 are so wound as tofunction in opposition to lamp current control winding 8.

Since the windings for heating the cathodes are connected subtractivelyto lamp current control winding 8, the inductances of windings 9 and 10reduce the inductance of the winding 8 for controlling the lamp current,and therefore the number of turns of winding 8 required to maintain apredetermined lamp current is remarkably increased as compared to thecase wherein the cathode heating windings are connected additively. Therequisite that the cathode heating voltage should be shifted correctlyby in relation to the lamp current is thereby satisfied to realize abalance of cathode spots.

According to the invention, since each winding is inserted in series asa single choke coil during the preheating period and the switch startmethod is adopted, lamp starting is reliable. Moreover, the cathodeheating windings are connected subtractively in relation to the lampcurrent control winding and can balance the cathode spots while heatingthe cathodes. Therefore, a higher output or longer life can be obtainedthan that obtained in the equal impedance system of the prior art. Allthe four windings can be wound around the same magnetic path, and thus acheaper lighting apparatus than that of the equal impedance system canbe provided, which is suitable in particular to a high output lightingapparatus for a fluorescent desk lamp.

We claim:

1. A high output operating apparatus for a fluorescent lamp of thecathode heating type and having a cathode at each end, comprising amagnetic circuit having a first and second outer leg and a center leg,two lamp current control windings wound, respectively, around said outerlegs, a compensation winding for cathode preheating and two cathodeheating windings wound around the center leg of the magnetic circuit,said cathode heating windings having low internal impedance, means forsupplying current to said lamp control windings and said compensationwinding before said lamp is operating, the flux in said center leg beingsuperposed to induce current in said two cathode heating .windings toprovide optimum preheating of the cathodes and excessive kick voltagebeing controlled by absorption of kick energy by secondary closedcircuits formed with said low internal impedance cathode heatingwindings, and for supplying current to said lamp control windings andsaid lamp while disconnecting said compensation winding during the timethe lamp is operating to form flux in the center leg by opposing thefluxes of the first and the second legs, said flux inducing heatingcurrent in said two cathode heating windings of a value subtractivelyrelated to the current in the lamp current control windings to provideoptimum cathode heating with the cathode heating voltage shifted 90degrees against lamp current in the low internal impedance cathodeheating windings, whereby cathode exhaustion by the cathode heatingeffect is reduced when said lamp is operating.

2. A high output operating apparatus for a fluorescent lamp of thecathode heating type having a cathode at each end, comprising twocathode heating windings having low internal impedance, a lamp currentcontrol winding, and a cathode preheating compensation winding woundaround the same magnetic path, and switch means for connecting eachwinding in series, when the lamp is preheated prior to operation of saidlamp, and, when the lamp is operating, to exclude the cathode preheatingcompensation winding from the circuit, means for supplying current tosaid series connected windings with said cathode preheating compensationwinding being connected withadditive polarity to the lamp currentcontrol winding to provide optimum preheating current and to controlexcessive kick voltage and for supplying current to said circuit withsaid cathode preheating compensation winding excluded, said circuit thenincluding said lamp current in opposition to said lamp control windingto provide optimum cathode heating voltage shifted degrees against lampcurrent in said low internal impedance cathode heating windings, wherebycathode exhaustion by the cathode heating effect is reduced.

3. A high output operating circuit for a fluorescent lamp of the cathodeheating type having a cathode at each end, comprising a common magneticcircuit; lamp current control winding means, a cathode preheatingcompensating winding, and a pair of cathode heating windings with lowinternal impedance, one for each cathode, coupled to said magneticcircuit; switch means having a first state for connecting saidcompensating winding between said cathodes for starting said lamp and asecond state for disconnecting said compensating winding from saidcircuit during operation of said lamp, means for supplying current, whensaid switch means is in said first state, to said lamp current controlwinding means, cathode preheating compensation winding and cathodeheating windings with said compensation winding being wound to provideoptimum preheating current and to control excessive kick voltage and forsupplying current, when said switch means is in said second state, tosaid lamp current control winding means, cathode heating windings, andsaid lamp with said cathode heating windings being opposed to said lampcurrent control winding means to provide optimum cathode heating voltageshifted 90 against lamp current in said low internal impedance cathodeheating windings, whereby cathode exhaustion by the cathode heatingeffect is reduced.

4. A circuit as recited in claim 3, wherein said common magnetic circuithas a pair of outer legs and a center leg, said lamp current controlmeans comprises a pair of windings wound, respectively, on said outerlegs, the flux from said pair of windings is in opposition in saidcenter leg, said preheating compensating winding and said cathodeheating windings are wound on said center leg, and the flux from saidpreheating compensating winding, when it is connected in the circuit, issuperimposed on the flux in the center leg.

5. A circuit as recited in claim 4, wherein said common magnetic circuitcomprises a pair of confronting E-cores.

6. A circuit as recited in claim 4, wherein said switch means comprisesa glow starter in series with said compensating winding.

7. A circuit as recited in claim 3, wherein said lamp current controlmeans comprises a lamp current control winding, and said switch means,when in said first state, connecting all of said windings in series withsaid cathodes.

8. A circuit as recited in claim 7, wherein said switch means comprisesa pair of manually operated switches, and wherein said switches, when insaid second state, connect said cathode heating windings across saidcathodes, respectively,

9. A circuit as recited in claim 7, wherein said cathode preheatingcompensating winding is wound additively with respect to said lampcurrent control winding.

1. A high output operating apparatus for a fluorescent lamp of thecathode heating type and having a cathode at each end, comprising amagnetic circuit having a first and second outer leg and a center leg,two lamp current control windings wound, respectively, around said outerlegs, a compensation winding for cathode preheating and two cathodeheating windings wound around the center leg of the magnetic circuit,said cathode heating windings having low internal impedance, means forsupplying current to said lamp control windings and said compensationwinding before said lamp is operating, the flux in said center leg beingsuperposed to induce current in said two cathode heating windings toprovide optimum preheating of the cathodes and excessive kick voltagebeing controlled by absorption of kick energy by secondary closedcircuits formed with said low internal impedance cathode heatingwindings, and for supplying current to said lamp control windings andsaid lamp while disconnecting said compensation winding during the timethe lamp is operating to form flux in the center leg by opposing thefluxes of the first and the second legs, said flux inducing heatingcurrent in said two cathode heating windings of a value subtractivelyrelated to the current in the lamp current control windings to provideoptimum cathode heating with the cathode heating voltage shifted 90degrees against lamp current in the low internal impedance cathodeheating windings, whereby cathode exhaustion by the cathode heatingeffect is reduced when said lamp is operating.
 2. A high outputoperating apparatus for a fluorescent lamp of the cathode heating typehaving a cathode at each end, comprising two cathode heating windingshaving low internal impedance, a lamp current control winding, and acathode preheating compensation winding wound around the same magneticpath, and switch means for connecting each winding in series, when thelamp is preheated prior to operation of said lamp, and, when the lamp isoperating, to exclude the cathode preheating compensation winding fromthe circuit, means for supplying current to said series connectedwindings with said cathode preheating compensation winding beingconnected with additive polarity to the lamp current control winding toprovide optimum preheating current and to control excessive kick voltageand for supplying current to said circuit with said cathode preheatingcompensation winding excluded, said circuit then including said lampcurrent control winding, said cathode heating windings, and said lampwith said two cathode heating windings being in opposition to said lampcontrol winding to provide optimum cathode heating voltage shifted 90degrees against lamp current in said low internal impedance cathodeheating windings, whereby cathode exhaustion by the cathode heatingeffect is reduced.
 3. A high output operating circuit for a fluorescentlamp of the cathode heating type having a cathode at each end,comprising a common magnetic circuit; lamp current control windingmeans, a cathode preheating compensating winding, and a pair of cathodeheating windings with low internal impedance, one for each cathode,coupled to said magnetic circuit; switch means having a first state forconnecting said compensating winding between said cathodes for startingsaid lamp and a second state for disconnecting said compensating windingfrom said circuit during operation of said lamp, means for supplyingcurrent, when said switch means is in said first state, to said lampcurrent control winding means, cathode preheating compensation windingand cathode heating windings with said compensation winding being woundto provide optimum preheating current and to control excessive kickvoltage and for supplying current, when said switch means is in saidsecond state, to said lamp current control winding means, cathodeheating windings, and said lamp with said cathode heating windiNgs beingopposed to said lamp current control winding means to provide optimumcathode heating voltage shifted 90* against lamp current in said lowinternal impedance cathode heating windings, whereby cathode exhaustionby the cathode heating effect is reduced.
 4. A circuit as recited inclaim 3, wherein said common magnetic circuit has a pair of outer legsand a center leg, said lamp current control means comprises a pair ofwindings wound, respectively, on said outer legs, the flux from saidpair of windings is in opposition in said center leg, said preheatingcompensating winding and said cathode heating windings are wound on saidcenter leg, and the flux from said preheating compensating winding, whenit is connected in the circuit, is superimposed on the flux in thecenter leg.
 5. A circuit as recited in claim 4, wherein said commonmagnetic circuit comprises a pair of confronting E-cores.
 6. A circuitas recited in claim 4, wherein said switch means comprises a glowstarter in series with said compensating winding.
 7. A circuit asrecited in claim 3, wherein said lamp current control means comprises alamp current control winding, and said switch means, when in said firststate, connecting all of said windings in series with said cathodes. 8.A circuit as recited in claim 7, wherein said switch means comprises apair of manually operated switches, and wherein said switches, when insaid second state, connect said cathode heating windings across saidcathodes, respectively,
 9. A circuit as recited in claim 7, wherein saidcathode preheating compensating winding is wound additively with respectto said lamp current control winding.